Conversion of maleic acid to fumaric acid



Patented May 11, 1 948 tion of New'Jersey- Chicago; 1111', a corpora,

No Drawing, Application lleccmbcr'-22,1944,, 'Seri'al'No. 569,419

6"Claim's. 1.

The present invention relates to a process for producing fumaric acid from maleic acid; and

particularly to a process whereby the maleic acid is converted in practically quantitative yields, to

fumaric acid of a high degree of purity.

The present application is a continuation-inpart of' myprevious application, Serial No. 486,- 4*49,-fi led'May 10, 1943', now abandoned.

It has been reported in the literature that f-uinaric acid results when maleic acid is heated alone or in aqueous solution. Various catalysts have'beenproposed for this transformation, such: as hydrochloric, hydriodic and-nitric acids and potassium thiocyanate.

The-process of the present invention is essentially an improvement in the method of carrying; out the-conversion through the agency of heat. I.

have found it possible to conduct the heating process so as to obtain a product which is essentially all fumaric acid; When carried outzim the presence of air or oxygen, however, such a;

process yields fumaric acid which is somewhat dark in color and, therefore, of little commercial value; fumaric acid can be purified by washing with water. This: treatment, although simple, does, of course, involve considerable and is accompanied with the inevitable loss, of product-indie solvent.

It is one of the objects of the present inventiicn to provide a process whereby maleic acid is convertedto funiaric acid by heat in such a mannenthat no subsequent purification of the prd-- uct is required. More specifically, the process involves: the heat treatment of maleic acid in a gaseous non-oxidizing medium to produce practically quantitative yields of fumaric acid oi a high degree of purity. The temperature can be varied over a wide range but I prefer to.

operate within the range 145-260 'C. Lower temperatures may beemplcyed but the rate of conversion then becomes too slow to be of commer-i cial value. Higher temperatures may. be. employed and the process has been operated. succes'siully at; the indicated temperature of 260 C. It is quite probable that by employin a flash process, even higher temperatures could beused to bring about the desired transiormation.,.

The primary object of the present invention is to produce an immediately saleable, dry fumaric acid from a form. of malcic acid, which comprises removing absorbed oxygen from the particular form of maleic acid which. isv employed as a starting material, confining the said form Of maleic acidin agaseousnon-"oxidizing attime and expense,v

I have found that such dark colored mosphere;andheating; it therein to a temperature;

within the above-mentioned range, for a time sufii'cient to convert substantially all of it into fum-aricacidof a high degree o'f'purity;

The term non-oxidizing atmosphere is used herein to denote an environment which is devoicr of oxygen assuchorin a form capable of oxidizing maleio acid or 'fumaricacid under the conditions employed duri-ng the conversion process. In addition to this, the non-oxidizing mediummust be such as not to act upon any of the possible intermediate products in a way to prevent the fin al formation of" fu'maric acid. Examples. of such- -non-0xidizing gaseous media: are nitrogen, carbon dioxide, hydrocarbonvapors', vapors of ethers, etci, which are nonreacti-ve with either ma leic 'orfumaric acids. I donot wish to be limited to-the'se examples since: other suitable non-oxidizin media will be readily apparent to those skilled in the art. Examples would be the inert gases such as helium, argon, neon, etc.

The function-f the non-oxidizing gaseous medium is. to v avoid. substantially all contact of: the reaction mixture with: oxygen.

Incarrying out. my process, I can. use as the starting material: either maleicacid or maleic: anhydride to which water. has been, added inamounts: at least. equal; to. that theoretically required to .iormzmaleic, aoidtherewith.

To illustrate the invention; more clearly, I: will;

now. describe; an. experiment which. demon..-- strates conclusively the advantages of employing a. process; involving the: use of a; non oxidizing atmosphere for, the conversion, of maleic acidinto fumaric acid.

For purposes of. comparison three containers were employed, These containers were made of glass and. each: received. aycharge of 1.0 parts by weight, of maleic acid; The first container was then sealedin air at atmospheric pressure; thus providing an atmosphere of. ordinaryair about the maleic acid.v A second container was treated, as follows: pure. oxygen gas was passed through the; container for about. one half hour in order to sweep out the air therein, and to insure the presence of an atmosphere of substantially: pure oxygen, whereafter the.- container, was sealed off. A, third container had. nitrogen. gas passed through'it for one half hour, in order to sweep out all traces of air and oxygen, Where'afterit was sealed oif.

The threecontainlers each containing 1.0, parts by weight of maleic acid, diiiened"from each other iii-the following" respects; in that the first container merely contained air at atmospheric pressure, the second container contained oxygen at atmospheric pressure, and the thind container contained nitrogen at atmospheric pressure. The three containers were placed in a suitable heating bath and heated tov a temperature between .195 and 210 0., being kept at that temperature for a period of two hours, after which the containers were cooled down, opened and the contents of each tube pulverized and examined.

It was found that in all been a substantial conversion of the maleic to the fumaric acid. This was not surprising, as theconversion of maleic acid to fumaric acid by heat is in itself well known. The difiiculties of the prior art methods, however, were plainly in evidence, particularly in connection with the first and the second tubes. In the fumaric acid which three cases there had was the result of heating container No. 1, which contained the air, was a product which was light tan in color, and which therefore would not have been immediately usable and saleable, and would have required recrystallization and other methods of purification, which would have entailed loss and expense. The second container, which contained the pure oxygen, produced a product which was of a dark tan color and therefore wouldhave required a considerable amount of purification, if in fact it could have been brought to a white condition at all.

On the other hand, the third container, which exemplifies the preferred embodiment of the present invention, produced a product which was dazzingly white, and which had a sharp melting point of 294 C. The melting point of the other two samples (i. e. from containers 1 andv 2) was not sharp and lay between 292 and 294 C. These samples were compared with an authentic sample of pure fumaric acid which melted sharply between 294 and 294.5 C. By making mixed melting point determinations, it was found that the products from the tubes containing air or oxygen lowered the melting point, while the product from the tube containing nitrogen showed no depression of the melting point of the authentic sample of the fumaric acid, this indicating the degree of purity of the product obtained in carrying'out the process of the present invention.

Other inert gases such as helium, neon, carbon dioxide, etc., may be substituted for the nitrogen. Similarly, the use of low boiling liquids in vapor form such, for example, as the vapor of ethyl ether and substantially inert hydrocarbons'such as 'rnethane, ethane, propane and butane, will yield results substantially like those obtained by the use of nitrogen.

For convenience, however, either nitrogen or carbon dioxide is the most practical gas for-the carrying out of the present invention. Applicant is aware of the fact that the mere thermal conversion of maleic acid into fumaric acid has long been known and also that the heating of maleic acid in aqueous solution results in the formation of some fumaric acid, means complete, and undesirable by-products form.

It had also beenjproposed in the prior artto convert maleic acid into fumaric acid while dise solved in benzene. However, under those conditions the maleic acid first passed into solution, then apparently became converted at least in part into fumaric acid, and eventually there was a formation ofiumaric acid. There was, however, still present a certain amount of unchanged but the reaction is by no maleic acid, and moreover it was necessary to remove the benzene from the formed fumaric acid, and to efiect an expensive and painstaking separation of the latter from any unchanged maleic acid. With applicants process, however, when worked between the limits of and 260 C., the conversion of the maleic acid to the fumaric acid is quantitative and the product obtained is pure white, dry and immediately saleable.

It is of course possible to utilize maleic anhydride as the starting point, adding the calculated'amount of water, placing the mixture in a sealed tube, and heating it in the inert gas. Under these conditions, the maleic anhydride becomes converted into maleic acid which then is converted, as a result of the heating, into the desired end product, that is, fumaric acid.

The exact apparatus to be employed is of course a matter of choice, and is well known to those familiar with chemical technology.

The term form of maleic acid" is used in the claims to cover both maleic acid itself or its an hydride in admixture with sufiicient water to hydrate it to maleic acid.

I claim:

1. Process of producing dry, pure white fumaric acid having a sharp melting point of about 294 C. from maleic acid which comprises placing maleic acid in a closed container, removing air from said container by means of an inert gaseous fluid and also thereby removing the adsorbed oxygen from said maleic acid, leaving an atmosphere of inert gaseous fluid in said container in contact with the maleic acid, and while maintaining said inert gaseous fluid in contact with the maleic acid, heating it to a temperature within the range of about 145 C. to about 260 C. until said maleic acid has been substantially completely converted into said pure White sharply melting fumaric acid.

2. The process as defined in claim 1 in which the maleic acid is initially dry.

3. The process as defined in the gaseous fluid is nitrogen.

4. The process as defined in claim 1 in which the gaseous fluid is carbon dioxide.

5. The process as defined in claim 1 in which the gaseous fluid is an aliphatic hydrocarbon vapor having less than 5 carbon atoms.

6. The process as definedin claim 1 in which the maleic acid is produced in situ from its anclaim 1 in which hydride by a sufficient quantity of water to convert said anhydride to maleic acid.

ANDREW P. DUNLOP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 974,182 Phelps Nov. 1, 1910 1,424,138 Bailey et al July 25, 1922 1,491,465 Craver Apr. 22, 1924.. 1,900,649 J aeger Mar. '7, 1933', 1,901,914 Livingston Mar. 21, 1933 2,208,519 Spence et al. July 16, 1940 2,315,529 Kelso Apr. 6, 1943 OTHER REFERENCES Gmelin, Handbook of Chemistry (Cavendish Tanatar, Liebigs Annalen, vol. 273, pages 31-36 Tomamusi et a1., Chemical Abstracts, vol. 32, (1893). page 500 (1938).

Pelouze, Beilstein, Handbuch der Organic Tomamusi et 2.1., Zeit Elektrochem, v01. 45, Chemistry, vol. 2, page 738 (1920). pages 72-79 (1939).

Beilstein, 4th ed. (1920), vol. 2, page 738. 5 Beilstein, 2nd Suppl. (4th ed. 1942), vol. 2, page Beilstein, 4th ed. (1929), vol. 2, page 300. 632.

Vaidya, Proc. Royal Society (London) A129, Pfeifier,Ber1chte (Deutsch. Chem. Gese11.),vo1. pages 299313 (1930). 47, page 1592.

Kistiakowsky et al., J. Am. Chem. Soc., vol. 54, pages 2208-2214 (1932). 

